SAN BRUNO (AP) — Federal investigators probing the cause of a deadly pipeline explosion in San Bruno said Friday they found dozens of defects and cracks in welds that held together segments of the pipe.
The decades-old welds could have failed after being weakened over the years by increases in pressure made to accommodate growing consumer demand, engineering experts who read the report told The Associated Press.
The National Transportation Safety Board previously determined the pipeline had experienced a spike in pressure just before the Sept. 9 blast in San Bruno that killed eight people and destroyed dozens of homes.
The report released Friday did not identify the cause of the explosion.
Pacific Gas & Electric Co., which owns the pipeline, said it was implementing all recommendations made by the NTSB to increase safety.
“All pipelines in PG&E’s system that are of a size and vintage similar to the line in San Bruno are continuing to operate at pressures that have been reduced by 20 percent — a measure that builds a significant additional margin of safety into our current operating conditions,” company president Chris Johns said.
The data released Friday will undergo further analysis by the NTSB, agency spokesman Keith Holloway said.
KCBS’ Mark Seelig Reports:
John Goglia, a former NTSB board member who read the report, said it provided evidence of significant problems with the welds.
“It was just generally poor quality welding,” he said.
The pipe varied in thickness in certain parts, and the report found the original welds had failed to penetrate completely in some areas.
Since the welds were made in 1956, before the use of X-rays to check integrity, it wasn’t possible at the time to know if there was a problem, Goglia added.
“As our demands for energy have increased, we’ve increased the pressure on pipes beyond what they were designed for,” he said.
The report also indicated there may have been multiple burst sites that led to the massive blast, said Robert Bea, an engineering professor at the University of California, Berkeley.
Because PG&E had increased pressure in the pipe a number of times in the past, Bea said it was likely the faulty welds were weakened a bit each time until finally giving way on Sept. 9.
He said the NTSB study found so many defects, he was surprised the problems were not discovered earlier.
“For me, it’s a bit of a miracle that the pipeline lasted this long,” Bea said.
U.S. Rep. Jackie Speier, D-Hillsborough, said the report revealed an important weak link in PG&E’s gas transmission system. She hoped it would spur more inspections to identify other weaknesses.
“The investigation does not preclude regulators and PG&E from taking action now to provide for the highest level of safety possible,” she said.
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